Potentiometer



April 30, 1963 T. LOCK POTENTIOMETER Filed Jan. 2s, 1961 United StatesPatent O This invention relates to potentiometers.

According to the present invention a potentiometer comprises an annularcasing, a helically wound resistance wire supported by the inner surfaceof the casing, a rotatable screw-threaded spindle extending axiallywithin the casing, and a carriage mounted on said spindle which ymovesaxially in response vto rotation of said spindle and carries anelectrical contact connecting the spindle and resistance wire.

The casing can be of any cross-section, including rectangular, squareand circular cross-sections.

In order that the invention may be more fully understood reference willnow be made to the drawing accompanying this specification in which:

FIG. 1 is a cross-sectional view of an embodiment of the invention; and

FIG. 2 is a view of FIG. 1 along the lines Il-IL Referring now to thedrawing a potentiometer comprises an annular casing 1 of insulatingmaterial which has a square cross-section and which supports a helicallywound resistance wire 2 secured to the inner surface of the casing.

One method of securing resistance wire 2 to casing 1 comprises providinga former of low melting point material, such as candle wax, Woods metalor Cerrobend of external dimensions just slightly less than the internaldimensions of casing 1 and winding resistance wire 2 in helical fashionon the external surface. The surface of the wire wound former and/or theinternal surface of casing 1 is then coated with a suitable adhesivesuch as Araldite and the lfor-rner is inserted within casing 1.Alternatively casing 1 can be moulded round the former. The turns ofresistance wire 2 can thus be made to adhere to the internal surface ofcasing 1 and the former can be thereafter removed by raising thetemperature sufficiently to cause it to melt. This leaves casing 1having resistance wire 2 helically wound around its inner surfaces.

An alternative method is to use a former of P.T.F.E. which has a slighttaper. The resistance wire 2 is Wound round the external surface of theformer secured to the internal surface of the casing as before. TheP.T.F.E. former can then be withdrawn from within the casing withoutinterfering with the winding.

Electrical contact with the ends of resistance wire 2 is provided bynarrow brass rings 14 and 15 which are a good fit on the former and areslipped over the former at either end to make contact with the ends ofthe resistance wires. External terminal leads 11 and 12 can then besoldered or welded to rings 14 and 15.

A rotatable screw-threaded spindle 3 extends axially within the casingand can be rotated by means of an insulating screw head 4 projectingbeyond one end of the casing. The other end of spindle 3 is supported bya spring-loaded ball bearing 5 which bears against a metal bearingsurface 6 in the lower end of the casing. A carriage 7 of insulatingmaterial such as nylon is mounted on spindle 3 and engages the threadthereof so that rotation of spindle 3 causes carriage 7 to move axiallyof the casing. Carriage 7 can be provided with a slit at one end toenable the threads to jump the threads of spindle Patented Apr. 30, 1963ice 3 when at either end of its run and thus prevent distortion of thethreads or casing.

Carriage 7 is provided with means for making electrical contact betweenresistance wire 2 and spindle 3. This means may comprise a hole drilledwithin carriage 7 extending radially of spindle 3 and carrying two ballbearings or metal caps 8 and 9 which are respectively held pressedagainst spindle 3 and resistance wire 2 by means of a spring 10 lyingbetween them.

The terminal leads 11 and 12 are brought out at one end of the casingand an external connection 13 is made to metal plate 6 and thus tospindle 3.

If an electrical potential difference is applied between terminals 11and 12 it will be appreciated that the potential on terminal 13 willdepend on the position of carriage 7 which can be varied by rotation ofscrew head 4.

While casing 1 is illustrated as being square it should be appreciatedthat it can be of any cross-section, although a square or rectangularcross-section allows a plurality of such potentiometers to be positionedside-by-side with a given range of resistance wire taking the leastroom. Furthermore the turns of winding 2 need not necessarily entirelyconform to the internal dimensions of casing 1. The casing can beenclosed in a metal can, which can be provided during moulding of thecasing.

What I claim is:

1. An electrical potentiometer comprising a casing formed of insulatingducting of polygonal section, a resistance wire wound helically aroundthe inner surface of the ducting, a rotatable conducting threadedspindle extending longitudinally within the wire, an insulating carriagein screw threaded engagement with said spindle and locked againstrotation by engagement with said inner surface, whereby rotation of thespindle is effective axially to move the carriage, a spring pressedelectrical contact mounted on the carriage and engaging adjacent turnsof the resistance wire, and means for electrically connecting thecontact with the spindle.

2. An electrical potentiometer comprising a casing formed of insulatingducting of rectangular section, a resistance wire wound helically aroundthe inner surface of the ducting, a rotatable conducting threadedspindle extending longitudinally within the wire, an insulating carriagein screw threaded engagement with said spindle and `locked againstrotation by engagement with said inner surface, whereby rotation of thespindle is effective axially to rnove the carriage, a spring pressedelectrical contact mounted on the carriage and engaging adjacent turnsof the resistance wire, and means for electrically connecting thecontact with the spindle.

3. An electrical potentiometer comprising a hollow member ofelectrically linsulating material having a bore, a helically wound wirecoil ixedly mounted in the wall of said bore, a threaded conductor rodrotatably mounted to extend longitudinally through the bore out ofcontact with said coil, a radially extending carriage of insulatingmaterial mounted in threaded engagement with said bore, and springbiased contact means extending through said carriage from the coil tothe rod, whereby rotation of said rod displaces said carriage axially ofsaid bore to determine the portion of said coil connected in electricalseries with the rod.

References Cited in the le of this patent UNITED STATES PATENTS

1. AN ELECTRICAL POTENTIOMETER COMPRISING A CASING FORMED OF INSULATINGDUCTING OF POLYGONAL SECTION, A RESISTANCE WIRE WOUND HELICALLY AROUNDTHE INNER SURFACE OF THE DUCTING, A ROTATABLE CONDUCTING THREADEDSPINDLE EXTENDING LONGITUDINALLY WITHIN THE WIRE, AN INSULATING CARRIAGEIN SCREW THREADED ENGAGEMENT WITH SAID SPINDLE AND LOCKED AGAINSTROTATION BY ENGAGEMENT WITH SAID INNER SURFACE, WHEREBY ROTATION OF THESPINDLE IS EFFECTIVE AXIALLY TO MOVE THE CARRIAGE, A SPRING PRESSEDELECTRICAL CONTACT MOUNTED ON THE CARRIAGE AND ENGAGING ADJACENT TURNSOF THE RESISTANCE WIRE, AND MEANS FOR ELECTRICALLY CONNECTING THECONTACT WITH THE SPINDLE.